Permanent magnet hot-wire starting device



Patented June 20, 1950 PERMANENT MAGNET HOT-WIRE STARTING DEVICE Stephen Eros, Cleveland, and Herman E. Hermanson, Mayileld Heights, Ohio, asslgnors to General Electric Com New York pany, a corporation of Application October 29, 1947, Serial No. 782,798

1 Claim.

This invention relates to electric switches and more particularly to a starting and operating switch for electric discharge devices, such as fluorescent lamps, using filamentary electrodes.

Circuits now in wide use with fluorescent lamps are provided with means for heating the filamentary electrodes and for impressing a high voltage for a short duration across the electrodes for starting an electrical discharge therebetween.

Some of these arrangements are provided with arrangements the delay means or switch provided relatively slow starting occasioned by lingering preheating periods, varying operating characteristics with age, and a slow reset operation for a recycle starting attempt. I

An object of our invention is to provide a new and improved circuit for starting and operating electrical discharge devices employing filamentary electrodes. F v

Another object of our invention is to provide a new and improved means for impressing starting voltages across filamentary electrodes of an electric discharge device which after a predetermined interval of time after the initiation of current flow through the electrodes impresses an operating voltage thereacross.

A further object of our invention is to provide a new and improved starting device for electric discharge devices which after a complete starting cycle of operation rapidly resets itself for another starting cycle.

A still further object of our invention is to provide a new and improved starting device for electric discharge devices which embodies a permanent magnet accurately controlled by a hot-wire thermal element.

Further features and advantages of our invention will appear from the following description of species thereof.

For a better understanding of our invention reference may be had to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims. Fig. 1 is a diagrammatic view of an electric discharge device and a starting and operating circuit therefore incorporating my in ventionf Fig. 2 illustrates in more detail a plan view of the permanent magnet, hot-wire starting device shown in the starting and operating circult of Fig. 1. Fig. 3 is a perspective view of the starting device shown in Fig. 2.

Referring to Fig. 1, we have there illustrated an electric discharge device I. The electric discharge device I, such as a fluorescent lamp, therein illustrated comprises an elongated tubular or cylindrical envelope 2 having sealed into the ends thereof filamentary electrodes 3 and 4, each herein illustrated as comprising a coil, preferably in the form of a'coiled coil of tungsten wire activated with oxides of alkaline earth metals such as a mixture of barium or strontium oxides. The envelope 2 contains a gaseous atmosphere such as a rare gas-like neon, argon or mixtures thereof at a pressure of a few millimeters and a small quantity of mercury which, during the operation of the lamps, has a low pressure of the order of 10 microns. The device I may be a low pressure positive column lamp of a fluorescent type provided with a suitable phosphor or fluorescent coating. This fluorescent coating upon excitation by the radiation produced by an electric discharge betweenthe electrodes, transforms a shorter wave radiation due to the discharge into longer wave radiation such as radiation within the visible range. For ease of starting a stripe or strip 5 of conductive material which, for example, may be a metallic paint or graphite mixed with potassium silicate, may be applied to the surface of device I. The starting strip 5 may be connected to one or both of the electrodes.

In accordance with our invention device I is connected across a suitable power supply circuit 6, 8' which for example may be a 115 volt, 60

' cycle source for supplying current to device I one embodiment of our invention as applied to through the usual ballast I which serves also as a starting inductance. A manual make-and-break control switch 8 may be used to connect device I to the power supply. A starting and operating circuit 9, 9 comprising a branch in series with device I and a branch in parallel with device I embodies a permanent magnet, hot-wire thermal snap-acting switch I0. Switch I0 comprises, in addition to a permanent magnet II and an expansible wire I2 having a high electrical resistivity and high coefllcient of thermal expansion, a spring armature "I3 pivoted to move to a position within the magnetic field of magnet II. One end of spring armature I3 is secured to the movable end of wire I2. Switch I0 comprises in addition a stationary contact I4 mounted on a supporting element IS, a movable contact I secured to an armature I1 provided with a curved or bent extension I8 of substantially U-shape and having a leg portion lying within the path of spring armature I3. An iron disc I9 may be mounted on the end of spring armature I3 which is secured to wire I2 in a position to permit movement within the magnetic field of magnet I'I.

amazes Wire it is connected to spring armature ii to oppose the bias of spring armature I! when cold and to permit when hot spring armature 53 to move within the magnetic field of magnet H. The series branch of the starting and operating circuit 9, 9' embodies ballast I in series with wire it, spring armature I8 and filamentary elec-- trodes I and 4 of discharge device i. The parallel branch of circuit 0, 9', operating as a starting circuit embodying normally closed contacts I6 and ii in series with filamentary electrodes 3 and l, shunts device i. A condenser 20 of a suitable value which for example, may be between 0.006 i. and 0.05 f. shunts device I and serves a dual function of preventing excessive arcing across contacts I4 and 16 upon opening thereof and reducing radio interference from device I.

When the entire installation is energized by closing manual make-and-break switch 8 current flows through ballast I, wire 12, spring armature i3, filamentary electrode 3, armature ii, movable contact l6, stationary contact ll, supporting element [5, and filamentary electrode '5. Wire H has a high electrical resistivity and high coefiicient of thermal expansion and thus expands with the passage of current therethrough. Spring armature i3 and wire l2 together act as a bow. When wire l2 expands upon the passage of current therethrough the tension oi spring I3 brings the iron disc is mounted thereon within the attraction range of the permanent magnet i I which snaps disc l9 into contact therewith. As disc I9 snaps into contact with magnet ii, extension 68 is engaged by armature i3 which causes movable contact id to separate quickly from stationary contact l4. Wire l2 while heating may permit spring armature I3 to move freely a predeter mined distance before it actuates extension i6 and moves within the field of magnet il. At the time contacts l4 and I6 disengage each other filementary electrodes 3 and l have reached the proper emission temperature and the interruption of the current fiow through ballast 7 causes a voltage surge great enough to cause an arc discharge to occur between electrodes 3 and 4 of device I.

The switch above described is selectively responsive to currents of two different predetermined values. For the smaller value of current, although wire [2 expands, it does not permit movement of the spring armature 13 to a position where the attractive force of the magnet ll exceeds the restraining force due to wire l2. When the larger value of current is transmitted through the wire l2, the expansion of the wire is greater thereby permitting the spring armature to move to a position where the attraction force of the magnet is greater than the restraining force of the wire. 1

While an arc discharge occurs in device i lamp current will flow through wire I2. Usually, lamp current is less than preheat current, so that wire 12 will not be as hot as it was during the starting operation. Wire l2 will contract somewhat, but, with the proper proportions between wire I2, spring armature l3, and magnet ll, this contraction will be insufllcient to pull spring armature l3 away from magnet Ii, over the normal variations of lamp currents and line voltages encountered under normal operation. Contacts I6 and 16 are thus held open while device I is operating.

When the arc discharge in device is interrupted by opening the manual make-and-break switch I. or if an arc discharge does not occur upon the initial opening of contacts it and i8, current no longer flows through wire it, and due to its low thermal inertia, wire l2 quickly cools, and in cooling contracts until the tension in. wire l2 overcomes the magnetic attraction for disc l9. Starter i6 is then ready for another starting cycle.

The ignition or starting device and circuits may be adjusted to the discharge device i in such a manner that if device i is faulty or non-operative the permanent magnet hot-wire switch it may be provided with additional lock-out means to operate after a predetermined number of starting attempts. Although the "look-out arrangement is not herein shown or described it may be ap= plied to this circuit.

Because of its low thermal inertia, a bare wire will usually expand too rapidly to allow proper preheat current to flow through electrodes 3 and l for a period of time long enough to provide adequate preheat. Improper preheating of the electrodes will shorten lamp life; therefore, we have found it desirable to coat wire it with an insulating material to increase its thermal inertia. A satisfactory combination for a 20-watt starting switch, for example, has been found to be a 5 mil nichrone wire with a 5 mil thick layer of glass fused thereto. If an 8 mil nichrome wire is used for a 20-watt starting switch, its thermal inertia would be satisfactory without insulating the wire.

It has been found desirable at times to decrease the ratio of holding force to pull-in force or magnetic attraction of magnet Hi. This may be accomplished by applying a thin layer of nonmagnetic low permeability material to the holding surface of magnet it or to disc 69. A transparent tape cemented to the holding surface of the magnet has been found to work satisfactorily.

Fig. 2 illustrates in more detail a plan view of the permanent magnet, hot wire starting device shown in the starting and operating circuit of Fig. 1. A support member 2i houses the components of the starting device. Contact terminals or pins 22, two of which are shown more clearly in Fig. 3 connect the starting device to the source of current andthe lamp filamentary electrodes.

Fig. 3 is a perspective view of the starting device shown in Fig. 2. Support member 2! houses the component parts of switch I0 wherein spring armature i3 is secured at one end of support member 2! and pivoted to move within the magnetic field of magnet it which is supported on the opposite end of member 2!. Armature i1 supporting movable contact IS on one end thereof is secured to support member 2i on the same end as spring armature it and pivots to make and break contact with stationary contact i4 secured to support member 2! on the opposite end thereof. Wire i2 is connected to spring armature i3 to oppose the bias thereof and is secured to support member 2! by means of a bracket 23 and an adjustment screw 26 which is used for supplying the proper operating tension to wire ii.

In accordance with our invention, we provide a starting and operating device and circuit which will a predetermined interval of time after the initiation of current flow through the electrodes impress an operating voltage thereacross. Accordingly, we provide a permanent magnet, starting device accurately controlled by a hotwire element. Furthermore, we provide a starting device which after a complete starting cycle 5 oi operation rapidly resets itself for another starting attempt.

Lastly, we provide a snap-acting thermal switch of the hot-wire type which is selectively responsive to currents of two difierent predetermined values, such as the preheating and operating currents of electric discharge devices employing filamentary electrodes.

What we claim as new and desire to secure by Letters Patent of the United States is:

In a control switch, support means, a fixed contact mounted on said support means, a strip having one end anchored to said support means and carrying a movable contact adjacent its free end, said strip being biased to hold said movable contact in engagement with said fixed contact and having at its free end a substantially U-shaped extension, a thermal expansible wire and a spring armature member joined together at one end and having their other ends supported from said support means in fixed superposed relation, said armature extending in the same general direction as said strip and having at its free end an extension projecting into the U-shaped extension on said strip, a permanent magnet mounted on said support means adjacent the free end of said armature and at the opposite side of said REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,859,985 Riedel May 24, 1932 2,133,309 Schmidinger Oct. 18, 1938 2,213,890 Schaefer Sept. 3, 1940 2,222,485 McCarthy Nov. 19, 1940 2,243,563 Hottenroth, Jr May 27, 1941 2,319,241 Leuthold May 18, 1943 2,338,875 Elkin Sept. 7, 1943 2,340,099 Acly et a1 Jan. 25, 1944 Alexander May 1, 1945 

